Creating solar panels that 'grow' in power

Okinawa
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Solar power is one of the key technologies for renewable sources of energy. Solar panels are limited by the amount of sunlight they absorb. Getting panels to hold more power is seen as key. Here could panels be developed so they grow in power?

This is the question that has been examined by scientists at the Energy Materials and Surface Sciences Unit (EMSS) at the Okinawa Institute of Science and Technology Graduate University (OIST), and they seem to have come up with an answer.

The answer is based around perovskite solar cells. These photovoltaic devices were introduced around 2006, and over the past ten years their efficiency has risen by over 22 percent. The term “perovskite” refers to the light-harvesting layer that configures the power within the cells. These types of solar cells are lighter, cheaper and more flexible than conventional crystalline silicon-based solar cells.

Through development it has been discovered that perovskite solar cells need to be exposed to ambient air for several hours after manufacture. This step has been shown to increase their efficiency. Until recently the reason why exposure to ambient was necessary has not been clear. The Okinawa Institute scientists now understand why.

The reason relates to the top layer of the solar cells, since this is the layer that is in contact with the circulating air and the one affected by variations in the external environment. This layer has been dubbed the “hole transport layer.” The layer contains a “dopant”, which refers to a substance that enhances the electrical conductivity of the material. This transport layer is the part that enhances the perovskite solar cell performance. The dopant in the transport layer is a type of salt called Lithium TFSI.

By varying the types of environmental gases that the dopant is exposed to, researchers have been able to enhance the efficiency of the solar cells still further. Variations to oxygen, nitrogen and moisture alter the transport layer. Of these, raising the moisture level helps the most to improve solar cell performance since it helps redistribute the dopant across the material surface. An effective redistribution improves the electric properties of the solar cell. Moisture needs to be controlled, however, since too long an exposure eventually damages the solar cell.

The research has been published in the journal Advanced Materials Interfaces. The research paper is titled “Moisture and Oxygen Enhance Conductivity of LiTFSI-Doped Spiro-MeOTAD Hole Transport Layer in Perovskite Solar Cells.”